1. Field of the Invention
The invention relates to a method for forming sheet metal, in which a blank is clamped in a parting plane between an upper tool and a lower tool with one of the tools having a shaped outline. The sheet metal is formed by an action of a hydraulic pressure medium acting against the sheet metal on a side opposite the shaped outline.
2. Description of the Prior Art
In addition to conventional mechanical deep-drawing for shaping sheet metal, methods are also known in which the acting medium is a hydraulic pressure medium. Thus, for example, in the so-called Hydro-Mec drawing method a sheet metal blank clamped between a sheet holder (hold-down device) and a drawing ring is forced by means of a shaping die, with the outline of the finished shaped part (workpiece), into a matching opposite tool, called a "water tank", in which the pressure medium is located and from which the pressure medium is forced (displaced) as the shaping die advances. This method has the advantage over purely mechanical drawing methods that the sheet metal blank is forced outward in the vicinity of the drawing radius of the drawing ring and consequently is not pulled over the drawing radius to avoid particularly high stress on the sheet metal blank. In addition, the exterior remains largely free of drawing marks. This method is not suitable for flat shaped parts with only a slight contour as a consequence of the finished shaped part (workpiece) having little dimensional stability.
Stretch forming produces flat shaped parts with a comparatively small wall thickness, in which the blank is clamped tightly between an upper tool and a lower tool. One of the tools has the desired shaped contour while the other tool is connected to a controllable hydraulic source. By acting on the blank on the side opposite the shaped contour, the blank is forced into the other tool. The forming is totally produced by stretching the sheet metal. The method is very limited both with regard to the degree of shaping and the thickness of the sheet that can be shaped.
Reverse stretch drawing is used to shape deeper contours in which one tool has a preform with less contouring while the other tool has the final shaped contour with both tools being activated by a pressure medium. The firmly clamped sheet metal blank is initially shaped by the pressure medium into the preformed tool and then given its final shaped contour by applying pressure from the other side. This method is very expensive to perform both in terms of tools and machinery.